1 /*- 2 * Copyright (c) 2001 Matthew Dillon. All Rights Reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16 * ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE 17 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23 * SUCH DAMAGE. 24 */ 25 26 /* Mutex pool routines. These routines are designed to be used as short 27 * term leaf mutexes (e.g. the last mutex you might acquire other then 28 * calling msleep()). They operate using a shared pool. A mutex is chosen 29 * from the pool based on the supplied pointer (which may or may not be 30 * valid). 31 * 32 * Advantages: 33 * - no structural overhead. Mutexes can be associated with structures 34 * without adding bloat to the structures. 35 * - mutexes can be obtained for invalid pointers, useful when uses 36 * mutexes to interlock destructor ops. 37 * - no initialization/destructor overhead. 38 * - can be used with msleep. 39 * 40 * Disadvantages: 41 * - should generally only be used as leaf mutexes. 42 * - pool/pool dependency ordering cannot be depended on. 43 * - possible L1 cache mastersip contention between cpus. 44 */ 45 46 #include <sys/cdefs.h> 47 __FBSDID("$FreeBSD$"); 48 49 #include <sys/param.h> 50 #include <sys/proc.h> 51 #include <sys/kernel.h> 52 #include <sys/ktr.h> 53 #include <sys/lock.h> 54 #include <sys/malloc.h> 55 #include <sys/mutex.h> 56 #include <sys/systm.h> 57 58 59 static MALLOC_DEFINE(M_MTXPOOL, "mtx_pool", "mutex pool"); 60 61 /* Pool sizes must be a power of two */ 62 #ifndef MTX_POOL_SLEEP_SIZE 63 #define MTX_POOL_SLEEP_SIZE 128 64 #endif 65 66 struct mtxpool_header { 67 int mtxpool_size; 68 int mtxpool_mask; 69 int mtxpool_shift; 70 int mtxpool_next; 71 }; 72 73 struct mtx_pool { 74 struct mtxpool_header mtx_pool_header; 75 struct mtx mtx_pool_ary[1]; 76 }; 77 78 #define mtx_pool_size mtx_pool_header.mtxpool_size 79 #define mtx_pool_mask mtx_pool_header.mtxpool_mask 80 #define mtx_pool_shift mtx_pool_header.mtxpool_shift 81 #define mtx_pool_next mtx_pool_header.mtxpool_next 82 83 struct mtx_pool *mtxpool_sleep; 84 85 #if UINTPTR_MAX == UINT64_MAX /* 64 bits */ 86 # define POINTER_BITS 64 87 # define HASH_MULTIPLIER 11400714819323198485u /* (2^64)*(sqrt(5)-1)/2 */ 88 #else /* assume 32 bits */ 89 # define POINTER_BITS 32 90 # define HASH_MULTIPLIER 2654435769u /* (2^32)*(sqrt(5)-1)/2 */ 91 #endif 92 93 /* 94 * Return the (shared) pool mutex associated with the specified address. 95 * The returned mutex is a leaf level mutex, meaning that if you obtain it 96 * you cannot obtain any other mutexes until you release it. You can 97 * legally msleep() on the mutex. 98 */ 99 struct mtx * 100 mtx_pool_find(struct mtx_pool *pool, void *ptr) 101 { 102 int p; 103 104 KASSERT(pool != NULL, ("_mtx_pool_find(): null pool")); 105 /* 106 * Fibonacci hash, see Knuth's 107 * _Art of Computer Programming, Volume 3 / Sorting and Searching_ 108 */ 109 p = ((HASH_MULTIPLIER * (uintptr_t)ptr) >> pool->mtx_pool_shift) & 110 pool->mtx_pool_mask; 111 return (&pool->mtx_pool_ary[p]); 112 } 113 114 static void 115 mtx_pool_initialize(struct mtx_pool *pool, const char *mtx_name, int pool_size, 116 int opts) 117 { 118 int i, maskbits; 119 120 pool->mtx_pool_size = pool_size; 121 pool->mtx_pool_mask = pool_size - 1; 122 for (i = 1, maskbits = 0; (i & pool_size) == 0; i = i << 1) 123 maskbits++; 124 pool->mtx_pool_shift = POINTER_BITS - maskbits; 125 pool->mtx_pool_next = 0; 126 for (i = 0; i < pool_size; ++i) 127 mtx_init(&pool->mtx_pool_ary[i], mtx_name, NULL, opts); 128 } 129 130 struct mtx_pool * 131 mtx_pool_create(const char *mtx_name, int pool_size, int opts) 132 { 133 struct mtx_pool *pool; 134 135 if (pool_size <= 0 || !powerof2(pool_size)) { 136 printf("WARNING: %s pool size is not a power of 2.\n", 137 mtx_name); 138 pool_size = 128; 139 } 140 pool = malloc(sizeof (struct mtx_pool) + 141 ((pool_size - 1) * sizeof (struct mtx)), 142 M_MTXPOOL, M_WAITOK | M_ZERO); 143 mtx_pool_initialize(pool, mtx_name, pool_size, opts); 144 return pool; 145 } 146 147 void 148 mtx_pool_destroy(struct mtx_pool **poolp) 149 { 150 int i; 151 struct mtx_pool *pool = *poolp; 152 153 for (i = pool->mtx_pool_size - 1; i >= 0; --i) 154 mtx_destroy(&pool->mtx_pool_ary[i]); 155 free(pool, M_MTXPOOL); 156 *poolp = NULL; 157 } 158 159 static void 160 mtx_pool_setup_dynamic(void *dummy __unused) 161 { 162 mtxpool_sleep = mtx_pool_create("sleep mtxpool", 163 MTX_POOL_SLEEP_SIZE, MTX_DEF); 164 } 165 166 /* 167 * Obtain a (shared) mutex from the pool. The returned mutex is a leaf 168 * level mutex, meaning that if you obtain it you cannot obtain any other 169 * mutexes until you release it. You can legally msleep() on the mutex. 170 */ 171 struct mtx * 172 mtx_pool_alloc(struct mtx_pool *pool) 173 { 174 int i; 175 176 KASSERT(pool != NULL, ("mtx_pool_alloc(): null pool")); 177 /* 178 * mtx_pool_next is unprotected against multiple accesses, 179 * but simultaneous access by two CPUs should not be very 180 * harmful. 181 */ 182 i = pool->mtx_pool_next; 183 pool->mtx_pool_next = (i + 1) & pool->mtx_pool_mask; 184 return (&pool->mtx_pool_ary[i]); 185 } 186 187 SYSINIT(mtxpooli2, SI_SUB_MTX_POOL_DYNAMIC, SI_ORDER_FIRST, 188 mtx_pool_setup_dynamic, NULL); 189